Our research endeavor is directed towards the eventual recovery of a virus or information about a possible virus associated with human cancer. By studying animal systems we hope to obtain information which will be helpful to the ultimate understanding of the cause of human malignancy. Our research activities will be concentrated on the following problems: 1) The eventual isolation of a non-virus producing murine sarcoma virus-transformed human cell for use in cocultivation studies with human leukemia cells. 2) Determining the efficiency of infection of human cells by Moloney sarcoma virus (M-MSV) and the characteristics of the sarcoma virus after several passages through human cells. 3) The characterization of the type "C" RNA virus in NZB mouse cells and the nature of the viral inhibitor produced by these cells. 4) The effect of thiosemi carbazones on murine RNA tumor viruses.